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KEY TERMS

INTRODUCTION

An ion is any atom that is missing electrons or has gained electrons. A hydrogen ion is formed by the loss of the electron; molecules that release hydrogen ions are called acids. Substances that readily combine with hydrogen ions are termed bases. In physiology, the concentration of hydrogen ions in body fluids is expressed in pH units. The pH of body fluids must be regulated (i.e., normal arterial blood pH = 7.40 ±.02) in order to maintain homeostasis. This regulation of the pH of body fluids is important because changes in hydrogen ion concentrations can alter the rates of enzyme-controlled metabolic reactions and modify numerous other normal body functions. Therefore, acid-base balance is primarily concerned with the regulation of hydrogen ion concentrations. High-intensity exercise can present a serious challenge to hydrogen ion control systems due to hydrogen ion production, and hydrogen ions may limit performance in some types of intense activities (7, 14, 16, 20, 40). Therefore, given the potential detrimental influence of hydrogen ion accumulation on exercise performance, it is important to have an understanding of acid-base regulation.

ACIDS, BASES, AND pH

In biological systems, one of the simplest but most important ions is the hydrogen ion. The concentration of hydrogen ions influences the rates of chemical reactions, the shape and function of enzymes as well as other cellular proteins, and the integrity of the cell itself (10, 46).